Accessibility: Improvements for the Authentication Check modal dialog "Close X".

Removes the title attribute and uses a `<button>` element instead of a `<div>`.
Also simplifies the CSS and takes care of the hover/focus style.

Fixes #35142.
Built from https://develop.svn.wordpress.org/trunk@36014


git-svn-id: http://core.svn.wordpress.org/trunk@35979 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -4934,7 +4934,7 @@ function wp_auth_check_html() {
 	<div id="wp-auth-check-wrap" class="<?php echo $wrap_class; ?>">
 	<div id="wp-auth-check-bg"></div>
 	<div id="wp-auth-check">
-	<div class="wp-auth-check-close" tabindex="0" title="<?php esc_attr_e('Close'); ?>"></div>
+	<button type="button" class="wp-auth-check-close button-link"><span class="screen-reader-text"><?php _e( 'Close dialog' ); ?></span></button>
 	<?php
 
 	if ( $same_domain ) {